Apart from using components that are implemented with a level of precision as high as possible, it is desirable, particularly in the area of microlithography, to adjust the position and geometry of optical modules of the imaging device, i.e. for example of the modules having optical elements such as lenses, mirrors or gratings, but also of the masks and substrates used, during operation as precisely as possible in accordance with specified setpoint values or to keep such components in their position once adjusted, in order to achieve a correspondingly high imaging quality (whilst the term optical module, in terms of the present disclosure, is to encompass both optical elements alone and assemblies made of such optical elements and further components, such as for example frame parts etc.).
In the area of microlithography, the desired level of precision is in the microscopic range in the order of just a few manometers or less. They are not least a consequence of the constant desire to enhance the resolution of the optical systems used for the manufacture of microelectronic circuits, in order to advance the miniaturisation of the microelectronic circuits to be produced.
In this connection it is known, amongst others, from US 2003/0234918 A1 (Watson), US 2007/0076310 A1 (Sakino et al.), U.S. Pat. No. 6,803,994 B1 (Margeson), DE 198 59 634 A1 (Becker et al.) as well as DE 101 51 919 A1 (Petasch et al.), the respective disclosures of which are incorporated herein by reference, to impose pre-defined deformations on individual or a plurality of optical elements of the system, in order to correct imaging errors of the imaging device. The deformation of the optical element concerned is here not only used to correct the respective optical element itself, but rather this is done in an attempt to compensate also for errors in the wave front, which are introduced by other components of the imaging device.
What can be problematic here is that the optical elements actively deformed in order to correct imaging errors as well as the other components involved in the deformation are not only exposed during operation to the usual thermal and dynamic loads, but, as a result of the deformation, also to further, partially substantial dynamic loads. These additional loads can have a negative effect on the lifetime of the optical element or of the other components involved in the deformation. Accordingly, these components of the imaging system generally are designed to be correspondingly robust and/or complex in order to meet the desired lifetime for the overall system. Moreover, optical elements having a larger cross section usually will have to be deformed. This in turn means that the actuators used are generally designed in such a way that forces that are appropriately high for a sufficient deformation are achieved.
A further problem, for example, in connection with the system known from US 2003/0234918 A1 (Watson) is that force actuators (for example Lorentz actuators) are used to generate the deformation, which force actuators themselves have a very low rigidity in their actuation direction and moreover act on the optical element via a system that is soft in the force flux direction, so that for small deformations of the optical element, comparatively long travel ranges are generally desired. As a result, a comparatively large installation space is generally desired for the deformation device, which can be of disadvantage in the light of the usually already confined spaces available.
A further disadvantage in connection with the known imaging systems can lie in the fact that, for the deformation of the optical elements concerned, a design of the support structure for the optical element which is specially adapted for this purpose is used. This means, if there is a wish to provide, in a pre-existing or fully designed optical imaging system, an optical element that has so far not been provided with such an active deformation with a corresponding deformation facility, then this will, as a rule, involve a complete re-design of the support structure for the optical element. This may, in certain circumstances, have an effect on the entire imaging system, if it is not possible to keep the position and the orientation of the optical element unchanged within the imaging system.
A further disadvantage of the imaging systems already known for example from US 2007/0076310 A1 (Sakino et al.) can lie in the fact that a quick success of the correction of imaging errors is largely dependent on the dynamic mechanical properties of the components involved in the deformation. Here, it is in principle particularly advantageous from a dynamic point of view if, amongst other things, the support structure that supports the deformation forces is designed to be particularly rigid (ideally infinitely rigid). The reason is that, in this case, a relative independence of the actuating movements of the individual actuators will be ensured, whereas the actuating movements of an actuator in the case of a less rigid support structure result in a deformation of the support structure, which influences the position and the orientation of at least the adjacent actuators, which in turn involves a correction within their region. As a result, a very complex control concept can become desirable, which can meet the desired dynamic properties in the field of microlithography only to a limited extent.